Cathode-ray tube



Patented Sept. 14, 1948 CATHODE-RAY TUBE George C. Sziklai, Princeton, N. J., assignor to Radio Corporation of America, a corporation of Delaware Application November 13, 1945, Serial No. 628,296

Claims.

This invention relates to cathode ray tubes for use in television and other applications.

In the usual television receiving tube one beam scans the phosphor target or screen and this is modulated in intensity at each elemental time by the received signals, so that each elemental area of the picture produced on the screen is bombarded once per line scansion by the beam with an intensity corresponding to the received video signals at that instant. This gives a line structure to the picture that is tolerated, but is nevertheless objectionable. It also limits the excitation of the elemental areas to the elemental time or the time of each picture signal,

It is an object of this invention to devise a cathode beam tube and scanning system that eliminates the line structure in the picture formed on the target.

Another object of the invention is to devise a television cathode beam tube in which the average brightness of the scanned elements of the target can be greatly increased above the saturation value of the target phosphor.

Another object of the invention is to produce a television tube in which each elemental area of the phosphor continues to fiuoresce from beam excitation after the signal for that area ceases.

Another object of the invention is to devise a television cathode beam tube in which a scanned element of the phosphor target luminesces at relatively high value during the time of the line scansion instead of during the time of the elemental area scansion.

Another object is to provide a cathode beam tube requiring decreased power for the line deflection plates or coils.

Another object of the invention is to provide a cathode beam tube for television purposes in which all the areas of a line are simultaneously bombarded by the beam at the beginning of the line scansion and is modulated for each elemental area of the line as the video signal arrives.

Another object of the invention is to provide a cathode beam tube in which a flat or ribbon-like beam of target line width scans the target through a control screen electrode in successive lines and another signal-modulated beam scans a line of the control screen electrode through which the flat beam passes, so as to place a signal-controlled potential thereon.

Other objects of the invention will appear in the following specification, reference being had to the drawings, in which:

Fig. 1 illustrates a cathode beam tube containing the invention.

Fig. 2 llustrates a modification.

Fig. 3 is a section of the tube taken on the line III-III of Fig. 2.

Fig. 4 is a cross-section diagram illustrating the modulated beam of the modification in Fig. 3.

Referring to 1 of the drawing, the evacuated envelope l contains a linear cathode C1, in front of which a grid 2 is placed to form the beam into a thin flat sheath or ribbon by means of the slit 3 under the accelerating force of first anode 9., having an appropriate slit 5 for passage of the sheath beam B1. The cathode may have a heater connected to heater terminals H1. H2. The parts described differ from those of the standard prior art tube in their being constructed so as to form a very thin flat beam of picture or raster line width and of thickness approximately equal to the height of the elemental area.

In the path of the beam is located an auxiliary control grid or screen 6 consisting of a plurality of spaced wires 1 imbedded in a frame 8 of poor dielectric or high resistive material, with a grounded conducting layer or plate 9 on the surface opposite the Wires. There should be substantially as many wires as the number of elemental areas in a line of raster, or the number should be proportional thereto. This grid construction is such that the closelyspaced wires have a high resistance and capacitative connection to ground through plate 9 for dissipation ofthe charges placed on the wires by another cathode beam.

The tube may have the usual wall coating l0, vertical deflecting plates H and phosphor target or screen I2. The grid 2 may be connected through a suitable negative bias source I 3 of suitable potential to the cathode C1 and the cathode C1 and capacity plate 9 may be grounded to one potential terminal, say negative,

. through a positive potential bias source 54. The

electrodes 4 and [0 may have suitable positive potentials, all as well understood in the art. The vertical deflection plates ll may be connected to the usual saw-tooth generator l5 having a frequency equal to the frame frequency to step the flat beam B1 vertically across the raster.

No means for scanning the beam B1 over the elemental areas of the line is required. To obtain equivalent scansion of the elemental areas of each line or" the target, a separate beam B2 is provided. The envelope l therefore contains a second gun l6 having the usual type of cathode ll, grid l8, anode l9 and wall coating 59, so positioned as to project a beam of usual elemental area size and shape onto the wires i of grid 6. Horizontal deflection coils 20, connected to a saw-tooth generator 2| of line frequency, move the beam B2 to scan the wires 1 and place charges thereon. The video signal is applied to the auxiliary grid [8 so that the intensity of beam B2 is varied in accordance with the signals as it scans the wires 1 in 'a' single line.

The operation of my invention will now be described:

The thin flat beam B1 may be visualized as composed of a plurality of elemental currents'impara-llel, one for each elemental area of a line. As this beam is projected onto the 'screen I 2, the electrons fluoresce to form a-luminous line across the raster, as at 22. The element-a1 areas of this line, assuming no m-odulation bybeam B2, would have substantially uniform luminescence. However, if the beam B2 is modulated by the video signals as it sweeps across the wires 1 of grid 6, charges varying with the signal will be' placed on the Wires and these-charges produce a potential that varies the elemental currents of the fiat beam, so that the elemental areas of line 22 hit by the modulated elemental currents of the beam B1 varyingly fiuoresce in accordance with the si nals for a time much longer than the time of each signal.

'Ihe'beam B1 thus is' projected simultaneously onto all the elemental areas of line 22, but it is modulated in sections in synch-ronism with the incoming signals. This varies the illumination, area by area, in accordance with such signals and the areas fiu-oresce duringthe'line scansion time instead of during the elemental area scansion time. When the beam Bi'finishes scanning a line, the saw-tooth voltage of the vertical deflecting plates l i'has 'moved the beam to the next line. In this way the entire picture area or raster is scanned. Since the beam B1 simultaneously strikes all elemental areas of a line, such a line 22, the viewer of the picture on the screen is not conscious of line structure'in the picture as he is with standard tubes, Where the beamtrace a varying bla-ck-to-white line.

In the usual television tube the elemental areas fluoresce only during the time the beam is thereon and thereafter phosphoresce in accordance with the decay characteristico-f the phosphor. The brightness also cannot be increased above a given value by increa-singthe beam current, because, as is Well known, phosphors have asaturation point. In my invention the same saturation point exists, but the brightness is increased because the elemental currents of the beam B1 can be made to impact the elemental areas so that the elemental areas fluoresce during the whole time of line scansion by proper choice'of the leak resistan-ce of-the grid 6. The eye integrate these values and the areas appear much brighter. Since the beam 132 is of less current value than the main beam B1, one is able to use lower power in the high frequency l-ine scansion coils 26, which is an obvious advantage.

Electromagnetic deflection means may be substituted for the electrostatic deflectionplates H and electrostatic deflection plates may besubstitu'ted for the electromagnetic coils 20, these being hown by Way of. example only.

Inthemodificaticn of Figs. 2 and '3, the same result is obtained by placing an auxiliary grid member 23, having a thin slit 24 similar to that of grid in line with the slit of that grid. This auxiliary grid is placed in front of the vertical deflection plates H. Between first anode i and the grid-member 23 isplaced plate 2510f glass or similar insulation material, or material of poor conductivity. Spaced from plate 25 on the opposite side of beam B1 i another plate 26 ,of conductive material. On or very closely adjacent to plate 25 is fine mesh screen 2? having the crossed strands or wires arranged preferably at angles of 45 and to the plane of beam B2. This angular position prevents resolution of the screen on the phosphor target. A suitable voltage is applied across the plate 26 and screen 2'! to position the beam B1 at the desired zero position. The screen 27 and cathode C1 are, as in Fig. 1, connected to ground through the positive biasing source M and the grid 6 is connected through the negative bias source 53 to cathode C1. The cathode C2 of the auxiliary gun is, like cathode C1, of Fig. l, of linear construction and is controlled by a grid 28 having a slit permitting a flat or ribbon-like beam B2 to be projected in a line onto the plate 25 through the screen 21. The beam is accelerated by an appropriate first anode 29 having a similar but somewhat larger slit pa allel to that in grid ill. The video signals are applied between. the grid 28 and ground through the usual negative bias source- Sc'l. Deflection plates 3! are connected to a saw-tooth generator 2i having the line frequency and the vertical deflection plates ii are connected to a saw-tooth generator it of frame frequency. Electromagnetic deflection may obviously be substituted for the electrostatic deflection in this modification.

The operation of the embodiment of Fig. 2 is as follows:

The flat beam B2 projects electrons in a line onto the plate 25 at a position depending upon the saw-tooth voltage applied to deflection plates 3 1. Secondary electrons are bombarded from the plate and are collected by screen 27, leaving a line of positive potential area under an elemental part of beam 131 that is proportional to the signal at that instant. This deflects that clemental part of the beam current a proportional amount, so that greater or less number of electrons are able to through the slit in grid 23. The elemental area. of target E2, in line 22, flucresces thereafter in accordance with this part of the beam until it is moved to the next line. At the next elemental time, beam B2 will move to another position, due to the saw-tooth voltage on deflector plates 36. Thi will move the next elemental portion of the beam B1 so that the electrons therein will pass through the slot in grid 23 in proportion to the positive charges in this new line on plate 25, that is, proportional to the signal on grid 28. In this way the hat beam is modulated in sections throughout its Width, as indicated in Fig. l.

The positive charges in the line in the plate Z5 will leal; off to the grounded screen within a line scansion time.

It is also permissible to use a pencil-like beam B2 in Fig. 3, as the charge would deflect the beam B1- so to vary the passage through grid 23, but the ribbondike beam B2 more powerful in its control of the beam 131.

Having described my invention, what I claim is:

1. In cathode ray tubes, an evacuated envelope containing a phosphor screen, a cathode, an anode, a grid, said anode and grid having slits adapted to form a flat beam from said cathode of thickness and width substantially equal respectively to the height of a picture element and the length of the picture line of said screen, deflecting plates positioned on opposite sides of said beam, one of said plates being of poor electrical conductivity, a mesh screen adjacent one side of the plate of poor conductivity, means for scanning the beam at frame frequency across said phosphor screen, a second cathode and means for forming and scanning a beam from the second-mentioned cathode across said mesh screen at line frequency.

2. In cathode ray tubes, an evacuated envelope containing a phosphor screen, a cathode, an anode, a grid, said anode and grid having slits adapted to form a flat beam from said cathode of thickness and Width substantially equal respectively to the height of a picture element and the length of the picture line of said screen, deflecting plates positioned on opposite sides of said beam, one of said plates being of poor electrical conductivity, a mesh screen adjacent one side of the plate of poor conductivity, means for scanning the beam at frame frequency across said screen, a second cathode, means for forming and scanning a beam from the second-mentioned cathode across said mesh screen at line frequency and means for signal-modulating the second-mentioned cathode.

3. In cathode ray tubes, an evacuated envelope containing a phosphor screen, a cathode, a grid and an anode for directing a beam of elec trons from the cathode to said phosphor screen, an auxiliary grid, said cathode, grids and anode having slits to form a fiat beam, a plate of poor electrical conductivity positioned parallel to said slits at one side of the beam between said anode and said auxiliary grid and means to scan signal voltages across said plate parallel to the direction of the width of said beam for deflecting the beam in elemental sections perpendicularly to the slit in said auxiliary grid.

4. In cathode ray tubes, an evacuated envelope containing a phosphor screen, a cathode, a grid and an anode for directing a beam of electrons e from the cathode to said phosphor screen, an auxiliary grid, said cathode, grids and anode having slits to form a flat beam, a plate of poor electrical conductivity positioned parallel to said slits at one side of the beam between said anode and said auxiliary grid and means for bombarding from said plate secondary electrons proportional to the received signals successively across said plate parallel to the direction of the width of said beam for deflecting the beam by the residual potentials in elemental sections perpendicularly to the slit in said auxiliary grid.

5. In cathode ray tubes, an evacuated envelope containing a phosphor screen, a cathode, a grid and an anode for directing a beam of electrons from the cathode to said phosphor screen, an auxiliary grid, said cathode, grids and anode having slits to form a fiat beam, a plate of poor electrical conductivity positioned parallel to said slits at one side of the beam between said anode and said auxiliary grid, a gun with means for producing a signal-modulated cathode beam and means for scanning said beam successively across said plate parallel to the direction of the width of said beam to bombard secondary electrons therefrom.

GEORGE C. SZIKLAI.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Number Name Date 2,111,941 Schlesinger Mar. 22, 1938 2,114,572 Ressler Apr. 19, 1938 2,118,865 Schlesinger May 31, 1938 2,179,205 Toulon Nov. 7, 1939 2,220,688 Schroter et al Nov. 5, 1940 2,259,506 Young et a1 Oct. 21, 1941 2,332,622 Calbick Oct, 26, 1943 FOREIGN PATENTS Number Country Date 494,145 Great Britain Oct. 18, 1938 513,099 Great Britain Oct. 3, 1939 

